Cellulose ethers
Cellulose ether molecule section (with R = organic residue) with the degree of substitution increasing from top to bottom. |
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Cellulose ethers are derivatives of cellulose that are formed by partial or complete substitution of the hydrogen atoms of the hydroxyl groups in the cellulose. This reaction is known as etherification .
properties
The properties of the cellulose ethers depend on the type of substituent, the number of substituted hydroxyl groups and their distribution. Cellulose ethers are thus soluble in water and / or organic solvents, depending on the type and number of ether groups introduced. Some cellulose ethers (e.g. methyl and hydroxypropyl celluloses) show reverse solubility in water, i.e. that is, they can be flocculated from their aqueous solutions by heating. Representatives of the group of cellulose ethers are z. B.
- Carboxymethyl cellulose (CMC)
- Methyl cellulose (MC)
- Ethyl cellulose (EC)
- Hydroxyethyl cellulose (HEC)
- Hydroxypropyl cellulose (HPC)
Cellulose ethers obtained by reacting cellulose with more than one etherifying agent are called mixed cellulose ethers z. B.
- Methyl ethyl cellulose (MEC)
- Hydroxyethyl methyl cellulose (HEMC)
- Hydroxypropyl methyl cellulose (HPMC)
- Ethyl hydroxyethyl cellulose
- Carboxymethyl hydroxyethyl cellulose
Different qualities with different property profiles are produced for the individual application areas.
Manufacturing
Cellulose ethers have been produced industrially since 1925, with water-soluble products becoming established. The aim of etherification is to incorporate hydrophilic substituents into the network of hydrogen bonds. The individual cellulose ethers are offered in a wide range of types, which result from the variables degree of substitution, degree of polymerization and solution viscosity. The manufacturing processes are optimized for the different properties of the cellulose ethers, but have the following common features in the basic steps:
- Pulp milling
- Activation of cellulose with concentrated caustic soda and formation of alkali cellulose
- Etherification with alkylating agents ( halogenated hydrocarbons (e.g. methyl chloride , ethyl chloride ), epoxides (e.g. ethylene oxide , propylene oxide ) or epichlorohydrin )
- Neutralization and washing out of by-products
- Processing and grinding or sieving of the end product
All etherification reactions carried out industrially on cellulose are carried out in a heterogeneous reaction, i. That is, there is no dissolution of the cellulose before or during the reaction. The cellulose is usually obtained from tree wood, whereby the lignin contained in the tree wood, initially z. B. must be separated from the cellulose structure as lignosulfonate . High quality celluloses can be obtained from cotton .
application
The market for cellulose derivatives (cellulose ethers and cellulose esters ) is estimated at over 100,000 t in Germany. The most important manufacturers are the groups DOW, Henkel and Shin-Etsu . In terms of quantity, the most important cellulose ether is carboxymethyl cellulose, followed by methyl cellulose and hydroxyethyl cellulose. The most important areas of application for cellulose ethers are building auxiliaries for the targeted adjustment of processing properties for gypsum, plaster, mortar and tile adhesive. Since cellulose ethers are products made from renewable raw materials, they are gaining in importance for environmentally friendly processes, e.g. B. as a textile auxiliary in the textile industry. Cellulose ethers are u. a. used as
- potential film formers
- Adhesives ( e.g. wallpaper paste )
- Emulsifiers
- Protective colloids
- Stabilizers
- Washing aids (there as dirt carriers and graying inhibitors) and hair conditioners
- Thickener for solutions based on water and organic solvents
They are used in a wide variety of areas such as
- Detergents and cleaning agents
- Cosmetics
- Pharmacy (USP Quality)
- Food and beverage industry (GMP quality)
- Adhesives, building materials and paints
- Textile, paper and cable industries
- Mining and oil production
- Agriculture
- Polymerization aid (e.g. PVC)
supporting documents
- ^ Wissenschaft-Online Lexika: Entry on cellulose ethers in the Lexikon der Chemie, accessed on March 17, 2010.
- ↑ H.-P. Fink and S. Fischer: Cellulose processing - environmentally friendly technologies on the advance. (PDF, 2MB) Fraunhofer Institute for Applied Polymer Research. In: Practical Science - Chemistry in School , Vol. 54 (2005), No. 7, pp. 18-25.
- ^ FNR [specialist agency for renewable raw materials] (2006): Market analysis of renewable raw materials; Gülzow.
literature
- Ullmann (4th) 9, 192-212
- Series of publications by the Fonds der Chemischen Industrie , Issue 24, pp. 71–76
- Römpp edition 1994
- Tanja Wüstenberg: Cellulose and cellulose derivatives. Behr's Verlag DE, 2013, ISBN 978-3-95468-188-4 , pp. 225-238 ( limited preview in the Google book search)